1. Field of the Invention
The present invention relates to a semiconductor light emitting device, and more particularly, to a semiconductor light emitting device that minimizes reflection or absorption of emitted light, maximizes luminous efficiency with the maximum light emitting area, enables uniform current spreading with a small area electrode, and enables mass production with high reliability and high quality.
2. Description of the Related Art
Semiconductor light emitting devices include materials that emit light. For example, light emitting diodes (LEDs) are devices that use diodes, to which semiconductors are bonded, convert energy generated by combination of electrons and holes into light, and emit light. The semiconductor light emitting devices are being widely used as lighting, display devices, and light sources, and development of the semiconductor light emitting device has been expedited.
In particular, the widespread use of cellular phone keypads, side viewers, and camera flashes, which use GaN-based light emitting diodes that have been actively developed and widely used in recent years, contributed to the active development of general illumination that uses light emitting diodes. Applications of the light emitting diodes, such as backlight units of large TVs, headlights of cars, and general illumination have advanced from small portable products to large products having high power, high efficiency, and high reliability. Therefore, there has been a need for light sources that have characteristics required for the corresponding products.
In general, a semiconductor junction semiconductor light emitting device has P-type and n-type semiconductor junction structures. In the semiconductor junction structure, light may be emitted by recombination of electrons and holes at a region where the two types of semiconductors are bonded to each other. In order to activate the light emission, an active layer may be formed between the two semiconductors. The semiconductor light emitting device having the semiconductor junctions includes a horizontal structure and a vertical structure according to the position of electrodes for semiconductor layers. The vertical structure includes an epi-up structure and a flip-chip structure. As described above, structural characteristics of semiconductor light emitting devices that are required according to characteristics of individual products are seriously taken into account.
FIG. 1A is a view illustrating a horizontal semiconductor light emitting device according to the related art. FIG. 1B is a view illustrating a vertical semiconductor light emitting device according to the related art. FIG. 10 is a cross-sectional view illustrating a vertical semiconductor light emitting device according to the related art. For the convenience of explanation, in FIGS. 1A to 1C, a description will be made on the assumption that an n-type semiconductor layer is in contact with a substrate, and a p-type semiconductor layer is formed on an active layer.
First, a horizontal semiconductor light emitting device will be described with reference to FIG. 1A.
A semiconductor light emitting device 1 includes a non-conductive substrate 13, an n-type semiconductor layer 12, an active layer 11, and a p-type semiconductor layer 10. An n-type electrode 15 and a p-type electrode 14 are formed on the n-type semiconductor layer 12 and the p-type semiconductor layer 10, respectively, and, are connected to an external current source (not shown) to apply a voltage.
When a voltage is applied to the semiconductor light emitting device 1 through the electrodes 14 and 15, electrons move from the n-type semiconductor layer 12, and holes move from the p-type semiconductor layer 10. Light is emitted by recombination of the electrons and the holes. The semiconductor light emitting device 1 includes the active layer 11, and light is emitted from the active layer 11. In the active layer 11, the light emission of the semiconductor light emitting device 1 is activated, and light is emitted. In order to make an electrical connection, the n-type electrode and the p-type electrode are located on the n-type semiconductor layer 12 and the p-type semiconductor layer 10, respectively, with the lowest contact resistance values.
The position of the electrode may be changed according to the substrate type. For example, when the substrate 13 is a sapphire substrate that is a non-conductive substrate, the electrode of the n-type semiconductor layer 12 cannot be formed on the non-conductive substrate 13, but on the n-type semiconductor layer 12.
Therefore, referring to FIG. 1A, when the n-type electrode 15 is formed on the n-type semiconductor 12, parts of the p-type semiconductor layer 10 and the active layer 11 that are formed at the upper side are consumed to form an ohmic contact. The formation of the electrode results in a decrease of light emitting area of the semiconductor light emitting device 1, and thus luminous efficiency also decreases.
In order to solve a variety of problems including the above-described problems, a semiconductor light emitting device that uses a conductive substrate, not the non-conductive substrate, appeared. A semiconductor light emitting device 2, shown in FIG. 1B, is a vertical semiconductor light emitting device. When a conductive substrate 23 is used, an n-type electrode 25 may be formed on the conductive substrate 23. In FIG. 1B, the n-type electrode is formed on the conductive substrate 23. Alternatively, after semiconductor layers grow by using a non-conductive substrate, the non-conductive substrate is removed. Then, an n-type electrode is directly formed on the n-type semiconductor layer, thereby manufacturing a vertical semiconductor light emitting device.
When the conductive substrate 23 is used, since a voltage can be applied to an n-type semiconductor layer 22 and the active layer 21 through the conductive substrate 23, an electrode can be directly formed on the substrate. Therefore, as shown in FIG. 1B, the n-type electrode 25 is formed on the conductive substrate 23, and a p-type electrode 24 is formed on a p-type semiconductor 20, a semiconductor light emitting device having a vertical structure can be manufactured.
However, when a high-power semiconductor light emitting device having a large area is manufactured, an area ratio of the electrode to the substrate needs to be high for current spreading. Therefore, light extraction is limited, light loss is caused by optical absorption, and luminous efficiency decreases.
In FIG. 1C, a horizontal semiconductor light emitting device has a structure that increases luminous efficiency. The semiconductor light emitting device 3, shown in FIG. 1C, is a flip chip semiconductor light emitting device. A substrate 33 is located at the top. Electrodes 34 and 35 are in contact with electrode contacts 36 and 37, respectively, which are formed on a conductive substrate 38. Light emitted from an active layer 31 disposed between an n-type semiconductor layer 32 and a p-type semiconductor layer 30 is emitted through the substrate 33 regardless of the electrodes 34 and 35. Therefore, the decrease in luminous efficiency that is caused in the semiconductor light emitting device, shown in FIGS. 1A and 1B, can be prevented.
However, despite the high luminous efficiency of the horizontal semiconductor light emitting device, the n-type electrode and the p-type electrode in the semiconductor light emitting device need to be disposed in the same plane and bonded. After being bonded, the n-type electrode and the p-type electrode are more likely to be separated from the electrode contacts 36 and 37. For this reason, there is a need for expensive precision processing equipment. This causes an increase in manufacturing costs, a decrease in productivity, a decrease in yield, and a decrease in product reliability.